Forbes then considered each influencer's potential for earnings per post, depending on the size of their following, their endorsement deals, and other business like product lines and book deals, to come up with the Top Influencers list, due to be published quarterly.

At 25 years old, Kayla Itsines is the most influential fitness star in the world.

9. Natalie Jill, 45.

Forty-five-year-old Natalie Jill started taking photos of her food during a struggle to lose post-pregnancy weight, and eventually developed a successful brand with a growing Facebook following. She now has e-books, DVDs, an app, a bestselling book, and runs video tutorials.

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8. Lyzabeth Lopez, 36.

Canadian-born Lopez is known for her "Hourglass Workout," which kicked off her business through Facebook a decade ago. While she now runs a successful gym franchise and an online training program, she told Forbes that she tries to remain authentic. "I turn down six-figure social media campaigns on a very regular basis due to not believing in the products," she said.

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7. Simeon Panda, 30.

Although he now has a sportswear line, a gym accessories brand, e-books, and a combined eight million followers on Instagram and Facebook — with a single video hitting over 600,000 views — Panda didn't start blogging until 2013, giving us all hope that it's not too late.

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6. Cassey Ho, 30.

Cassey Ho's success includes the books, DVDs, a line of working clothing and accessories, and a YouTube channel, which she launched in 2009. Ho, 30, told Forbes that she originally posted her pilates workouts for her students to watch, though they became popular amongst a much wider audience.

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5. Joe Wicks, 31.

Social media star Joe Wicks, or "The Body Coach" as he is known to his followers, has built a fitness empire on showing people how to get "Lean in 15." He started out on Twitter, according to Forbes, and now has an audience of five million, spending "every waking hour" working on his brand.

His concept is based on HIIT workouts and 15-minute recipes, which he shares through quick and snappy Instagram videos and cookbooks, which are tasty and easy to put together, yet part of a diet plan that he credits for his own fit lifestyle.

4. Michelle Lewin, 31.

Venezuela-born bodybuilder Michelle Lewis earns as much as $10,000 per Instagram post, according to Forbes. She has partnerships with a number of brands, but with 14 million followers across her accounts, a line of supplements, and a range of workout equipment, her time is limited.

"I am too busy with my own brands, and I have just started," she told Forbes.

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3. Emily Skye, 32.

Now the brains behind a successful online workout program, an app, video tutorials, a makeup line, and an upcoming sneaker collaboration with Reebok, Skye told Forbes that her social media following kicked off in 2011.

"I had a Blogspot page where I shared my meals and workouts and my experience competing in fitness competitions," she said.

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2. Jennifer Selter, 23.

Originally working the front desk at a gym, Selter now runs seven Instagram accounts, including her successful personal @jenselter, @couplegoals, and @thatbikini, and is about to launch a line of workout gear.

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1. Kayla Itsines, 25.

At only 25, Itsines is the most influential fitness star in the world, selling out stadium tours in an hour. According to Forbes. Her "Sweat With Kayla" app generated $17 million in revenue last year, according to App Annie.